Acid drainage: the global environmental crisis you’ve never heard of

Romania’s prime minister, Mihai Tudose, recently raised the prospect of reopening the country’s huge Roșia Montană goldfield. The area had been mined from Roman times until the last state-run operation closed in 2006. An application by a previous government to make the area a UNESCO world heritage site has now been withdrawn, paving the way for new development.

Roșia Montană is nestled in the Carpathian mountains and, with 314 tonnes of gold, has Europe’s largest known deposits. A short-term mining bonanza promises employment for thousands of labourers and hundreds of millions of Romanian Leu in investment in the EU’s fastest-growing economy. But is the boom really worth it? After all, gold mining has historically resulted in long-term, chronic environmental problems. Roșia Montană is big, but the threats posed by acid mine drainage are bigger.

The problem is, if completed, the so-called Roșia Montană project would use “cyanide amalgamation” to extract the gold from its ore body. This is the same cyanide used to poison people, fish and elephants. It has a toxic past in Roșia Montană, too: back in the 1970s, a copper mine in the area needed somewhere to store its cyanide-contaminated waste and the nearby village of Geamana was evacuated and flooded. It has been submerged under toxic waters ever since.

A single church spire pokes through the toxic waters: all that remains of Geamana.Calin Stan / shutterstock

Gold’s dirty secret

Cyanidation was the breakthrough gold mining technology of the 1890s, when it enabled Anglo mining conglomerates to make colossal profits from low grade ores. Simply put: cyanidation involves mixing finely crushed ores (referred to as “sands” or, when water-based, “slimes”) in a weak cyanide solution (usually calcium cyanide). This solution is then mixed in large tanks and the gold separated from its ore body.

The process increases yields of gold but produces immense quantities of highly-toxic waste that releases acid and metals into the environment. Around 90% of all gold extracted worldwide uses this method.

Waste water from a gold mine flows into the forest. Guyana, South America.kakteen / shutterstock

The waste from cyanidation is a fine rock solution that is left in open air ponds while the concentration of acid is reduced to legal limits. The risk here is from dam failure or breakages in the lining of waste ponds, which can lead to catastrophic spills or leakage through the porous land surface into the water table.

In nearly all metal mines, and some coal mines, acid drainage occurs because of the oxidation of iron ore found alongside precious mineral deposits. Uncovered by the mining process, the iron reacts with the air and releases sulphuric acid into the water. This process can last centuries. Spills from cyanidation waste are more short-lived, but more highly toxic than acid mine drainage occurring through iron oxidation.

The ratio of waste to metal recovered in gold mining is vastly disproportionate: the Fimiston Super Pit, near the West Australian town of Kalgoorlie, and until recently the largest open cut mine in the world, has returned approximately 1,640 tonnes of gold since operations began there in 1989. But that’s only a small portion of the 15m tonnes of rock extracted per year. A typical gold wedding ring will generate about 30 tonnes of waste.

The river runs yellow

In 2015, as the US Environmental Protection Agency attempted to drain polluted water from the Gold King Mine, Colorado, which was closed in 1920, more than 3m gallons were accidentally spilled into the Animas River. The polluted plume turned the entire river a deep mustard yellow. Water acidity levels increased 100-fold, and in some places a thousand times over levels considered safe for wildlife.

The spill only posed no threat to fish in the Animas because ongoing pollution had already killed them. But the plume drained into the San Juan, a larger and cleaner river that flows into the spectacular Glen Canyon and, eventually, the Grand Canyon. There, the pollution threatened rare birds and endangered fish like the Colorado pikeminnow and razorback sucker.

The Animas River as normal, on the day of the Gold King Mine spill (L), and a day later ®.Barbara K Powers / shutterstock

EPA chief Scott Pruitt returned to the site at the beginning of August this year vowing to complete the clean-up after the agency had “walked away” from the problem. At a water treatment plant installed on the site, 500 gallons of mercury and arsenic-laced water a minute flow from the Gold King Mine. The clean-up could take a decade and has already cost the EPA US$29m. The EPA has estimated that the cost of cleaning up just 156 mines in the US could be between US$7billion and US$24 billion. Clean-up on most sites will take decades – those with acid drainage will require water treatment in perpetuity.

A global crisis

Acid drainage is a little-known global crisis. The UN has even labelled it the second biggest problem facing the world after global warming. In the US, an estimated 22,000km of streams and 180,000 acres of freshwater reservoirs are affected by acid mine drainage. Rivers and lakes in Arizona, Patagonia, Guangdong (China), Ontario, Papua New Guinea, and at Rio Tinto in Spain, to name just a few, have all been polluted by acid mine drainage. In South Africa, the problem is chronic.

These threats are prescient. Brazil recently announced a huge reserve in the Amazon rainforest has been earmarked for mining, including gold. In New Zealand, local activists fear the Karangahake Gorge is now under threat after a large, high-quality gold seam was found in the region. Around the Yellowstone National Park, mining companies are positively salivating at the possibility that Obama-era restrictions will be lifted, granting access to 3,000 tonnes of proven in-ground gold reserves. In Peru, marines have been dispatched to wage war against illegal mining on the River Santiago in the northern Amazon, which has done enormous damage to the region’s bio-diversity and placed the livelihoods of 70,000 indigenous Awajúns and Wampís at risk.

Multinationals hold out the promise of sustainable development through mining. But without careful forethought we’ll find ourselves dealing with chronic pollution for centuries.